Generally, the vocal folds of a human body are vocal organs for communication by a language, and a laryngeal mucosa vibrates about 100 to 250 times per second according to respiration. In other words, air inhaled into a lower airway pressurizes vocal folds closed in a sub-glottal area. When the pressure is greater than a resistance of the vocal folds, a mucosal wave propagating from an inferior margin of the vocal folds to a superior margin thereof is generated, and the vocal folds open to start vocalization. When the pressure is lowered, the vocal folds are closed. This is repeated 100 to 250 times per second to produce a voice.
However, in the case of vocal fold nodules, glottic cancer, vocal fold paralysis, and the like, effective energy conversion of the sub-glottal part is impossible and symmetry of mucosal waves is degraded, leading to an abnormal voice.
Therefore, when abnormality of the voice is diagnosed, it is necessary to identify a motion state of the vocal-fold mucosae. To this end, a method of identifying a motion state of vocal-fold mucosae using stroboscope technology has been developed. Currently, a method using laryngeal videostroboscopy for observing rapid motions of 100 to 250 times per second at slow motion using stroboscopic technology is primarily used. However, a laryngeal videostroboscopic image does not actually show vibrations of vocal folds and is an image obtained by combining some frame images among vocal-fold vibration images of several periods captured at about 20 to 30 frames per second into one period to slowly show motions of the vocal folds. Also, a laryngeal videostroboscopic image has a disadvantage in that accurate motions of vocal folds cannot be acquired as an image when it is not possible to continuously vocalize for five or more seconds or vocalization is irregular.
Much research has been conducted to overcome these disadvantages of laryngeal videostroboscopy, and an ultra-high speed digital video system disclosed by Hirose et al. photographs vocal-fold vibrations at 2,000 frames or more per second and is used as a practical diagnosis tool for evaluating vocal-fold vibrations.
Also, methods of generating a videokymography image by post-processing an image acquired from an ultra-high speed camera and analyzing a mucosal motion state by comparing and observing vibrations of both vocal folds have been developed. However, currently developed videokymographic images have problems in that only a kymogram of one line or multiple lines can be obtained and it is not possible to observe a motion state of an entirety of vocal-fold mucosae from the kymogram.
Recently, Wang et al. has devised a system for observing vibrations of an entirety of vocal folds using the principle of laryngeal photokymography of Gall et al., and has developed two-dimensional scanning videokymography (2D VKG) for examining a vibration state of the entirety of the vocal folds in real time. 2D VKG may avoid distortion caused by a motion of a patient and the like and also enable an analysis of a mucosal motion state through comparative observation of entire regions of both vocal folds.